The present invention generally relates to an electromagnetic tracking system. In particular, the present invention relates to an electromagnetic tracking system with an electromagnetic coil array integrated into an antiscatter grid.
Many medical procedures involve a medical instrument, such as a drill, a catheter, scalpel, scope, stent or other tool. In some cases, a medical imaging or video system may be used to provide positioning information for the instrument, as well as visualization of an interior of a patient. However, medical practitioners often do not have the use of medical imaging systems when performing medical procedures. Typically, medical imaging systems are too slow to produce useable real-time images for instrument tracking in medical procedures. The use of medical imaging systems for instrument tracking may be also limited for health and safety reasons (e.g., radiation dosage concerns), financial limitations, physical space restrictions, and other concerns, for example.
Medical practitioners, such as doctors, surgeons, and other medical professionals, often rely upon technology when performing a medical procedure, such as image-guided surgery or examination. A tracking system may provide positioning information of the medical instrument with respect to the patient or a reference coordinate system, for example. A medical practitioner may refer to the tracking system to ascertain the position of the medical instrument when the instrument is not within the practitioner's line of sight. A tracking system may also aid in presurgical planning.
The tracking or navigation system allows the medical practitioner to visualize the patient's anatomy and track the position and orientation of the instrument. The medical practitioner may use the tracking system to determine when the instrument is positioned in a desired location. The medical practitioner may locate and operate on a desired or injured area while avoiding other structures. Increased precision in locating medical instruments within a patient may provide for a less invasive medical procedure by facilitating improved control over smaller instruments having less impact on the patient. Improved control and precision with smaller, more refined instruments may also reduce risks associated with more invasive procedures such as open surgery.
Tracking systems may also be used to track the position of items other than medical instruments in a variety of applications. That is, a tracking system may be used in other settings where the position of an instrument in an object or an environment is unable to be accurately determined by visual inspection. For example, tracking technology may be used in forensic or security applications. Retail stores may use tracking technology to prevent theft of merchandise. In such cases, a passive transponder may be located on the merchandise. A transmitter may be strategically located within the retail facility. The transmitter emits an excitation signal at a frequency that is designed to produce a response from a transponder. When merchandise carrying a transponder is located within the transmission range of the transmitter, the transponder produces a response signal that is detected by a receiver. The receiver then determines the location of the transponder based upon characteristics of the response signal.
Tracking systems are also often used in virtual reality systems or simulators. Tracking systems may be used to monitor the position of a person in a simulated environment. A transponder or transponders may be located on a person or object. A transmitter emits an excitation signal and a transponder produces a response signal. The response signal is detected by a receiver. The signal emitted by the transponder may then be used to monitor the position of a person or object in a simulated environment.
Tracking systems may be ultrasound, inertial position, or electromagnetic tracking systems, for example. Electromagnetic tracking systems may employ coils as receivers and transmitters. Typically, an electromagnetic tracking system is configured in an industry-standard coil architecture (ISCA). ISCA uses three colocated orthogonal quasi-dipole transmitter coils and three colocated quasi-dipole receiver coils. Other systems may use three large, non-dipole, non-colocated transmitter coils with three colocated quasi-dipole receiver coils. Another tracking system architecture uses an array of six or more transmitter coils spread out in space and one or more quasi-dipole receiver coils. Alternatively, a single quasi-dipole transmitter coil may be used with an array of six or more receivers spread out in space.
The ISCA tracker architecture uses a three-axis quasi-dipole coil transmitter and a three-axis quasi-dipole coil receiver. Each three-axis transmitter or receiver is built so that the three coils exhibit the same effective area, are oriented orthogonal to one another, and are centered at the same point. The exact sizes, shapes, and relative-to-one-another positions of the transmitter and receiver coil-trios are measured in manufacturing. If the coils are small enough compared to a distance between the transmitter and receiver, then the coil may exhibit dipole behavior. Magnetic fields generated by the trio of transmitter coils may be detected by the trio of receiver coils. Nine transmitter-receiver mutual inductance measurements may be obtained. From these nine parameter measurements and the information determined in manufacturing, a position and orientation determination of the receiver coil-trio may be made with respect to the transmitter coil-trio for all six degrees of freedom.
Some existing electromagnetic tracking systems include a transmitter and receiver wired to a common device or box. In system with the transmitter and receiver wired to a common device, the object being tracked is wired to the same device as the components performing the tracking. Thus, the range of motion of the object being tracked is limited.
Wireless electromagnetic tracking systems allow for the object being tracked to move freely without being limited by connections with the transmitter or receiver. To reduce the bulk associated with attaching a battery or other power source to a transponder, passive transponders may employ a coil as a means of coupling with and receiving power from other devices.
Typically, a transponder is located on or within a device in order to track movement of the device. In order to determine the transponder's location, a transmitter generates an excitation signal that is incident on the transponder. The incidence of the excitation signal on the transponder causes the transponder to emit a response signal. Typically, the response signal is emitted at the same frequency as the excitation signal.
The response signal emitted by the transponder and the excitation signal emitted by the transmitter are incident upon a receiving coil. Typically, in a tracking system using a passive transponder the excitation signal is much larger than the response signal when both signals are received at the receiver. Because the response signal is emitted at the same frequency as the excitation signal and the response signal is much smaller than the excitation signal, accurately separating and measuring the response signal is difficult.
When using an electromagnetic tracking system to track the position and orientation of an x-ray detector in a fluoroscope, for example, an electromagnetic coil array (transmitter or receiver) is typically mounted on the detector assembly. More particularly, the electromagnetic coil array is typically mounted on the outside of the detector assembly. For example, Anderson et al. (U.S. Pat. No. 6,774,624), Seeley et al. (U.S. Pat. Nos. 6,484,049, 6,490,475, 6,856,826 and 6,856,827), Ferre et al. (U.S. Pat. No. 6,445,943), and Jascob et al. (U.S. Pat. No. 6,636,757) disclose electromagnetic coil arrays mounted on the outside of the detector assembly. In particular, Jascob et al. (U.S. Pat. No. 6,636,757) provides that “offsetting the set of transmitting coils 62 from the shield 54 creates less inteference or cancelling of the electromagnetic field because of the shield 54, to provide enhanced performance.” Additionally, Ferre et al. provides that “since the presence of magnetic material might interfere with the magnetic fields these materials are to be avoided in such an electromagnetic system.”
Furthermore, modern x-ray detectors, such as amorphous silicon flat-panel x-ray detectors, typically do not include enough space for mounting an electromagnetic coil array on the inside of the detector assembly (where the electromagnetic coil array would be in the field of view of the detector, and thus, most effective). As such, current electromagnetic coil arrays typically include a small coverage area and are offset from the detector. Consequently, the patient or detector (including the electromagnetic coil array) must be repositioned several times, thereby inconveniencing the patient and wasting valuable time, money, and other valuable resources.
Thus, a need exists for an electromagnetic coil array in the field of view of an x-ray detector. More particularly, a need exists for an electromagnetic coil array integrated into an antiscatter grid.